One of the staples of desktop web browsing may be coming to iOS with a new feature Apple is adding to Safari with a forthcoming update to its mobile operating system.

Safari on iOS 9 will include support for "Content Blocking" extensions that, when installed, will remove content from a web page based on a list created by a developer. According to Apple's sparse documentation, the functionality can be used to block "cookies, images, resources, pop-ups, and other content." In theory, that should pave the way for ad blocking browser extensions on the iPhone and iPad that users can employ to remove ads from their experience of the internet.

If that comes to pass, it could mark a big shift in the way advertisers think about mobile traffic, which continues to grow as an overall percentage of total web traffic. iOS devices are valuable targets for ads, and if users are able to block them, that could put advertisers, and hence publishers and website operators, at a significant disadvantage.

From a consumer standpoint, removing ads makes sense. They're intrusive, distracting, and often involve invasive tracking that conflicts with a desire for privacy. Ad blocking tools are among the most popular browser extensions precisely because they handle all of those nuisances in one convenient package.

A recent study from the University of Pennsylvania's Annenberg School for Communication showed that Americans don't want to give up their privacy to marketers, but feel like they don't have a choice. Ad blocking provides them with a means to get some of that control back -- even if it's ham-fisted.

But blocking ads also means users are depriving publishers and other free web services of revenue they use to keep the lights on. The prevalence of ad blocking extensions like AdBlock Plus on desktop platforms has proven problematic for publishers and led to the rise of native advertisements that don't stand out as much as traditional banner ads.

Still, Apple's blocking system may hold more peril than promise for ad blocking software. At the moment, ad blockers watch a user's browsing session and employ complex rules in order to clear out advertisements. While that allows them to effectively block users from seeing advertisements, it also means that they have permission to see everything a user does on the web.

The system that Apple is implementing in Safari on iOS and OS X with its upcoming software releases works differently. Instead of allowing an extension to go through a web page and remove elements from it, a content blocking extension provides Safari with a list of content to block, which the browser applies as it loads a web page. It doesn't provide any feedback to the extension, which means that developers won't be able to track what users do.

It would seem to be bad news for Ghostery, a popular ad blocking extension that makes money by providing advertisers with anonymized information about what sort of tracking it blocked its users from encountering during their browsing sessions.

According to AdBlock Plus developer Sebastian Noack, the new Content Blocking extensions will work very differently from how AdBlock Plus works today, and could prove incredibly useful, but only if the block lists Apple is introducing are powerful enough.

"In short, either this new API will improve Adblock Plus performance on Safari or it will force us to rely upon an inferior blocking format that would essentially kill adblocking on Safari," he wrote.

Unfortunately, the extensions don't even seem to work on the current developer beta of iOS 9, and Apple's documentation at this point is minimal at best. It's hard to say exactly what will come of the functionality.

Allowing any kind of content blocking makes significantly more sense for Apple than it does for the company's largest competitor in the smartphone market. Google makes the overwhelming majority of its money selling advertisements on the web, which means that people who block advertisements cut directly into its business. Apple operates its own iAd network, but those advertisements don't show up in web content, and the company makes most of its money from selling high-end hardware at a profit.

Facilitating ad blockers could make consumers happier with Apple, while also hurting one of its biggest rivals, which would be a win for the iPhone maker. However, the decision would also hurt websites like those run by news organizations that publish their content for free and rely on advertisements to pay for it, along with other free web services that count on ads to make money.

These changes come as Apple seeks to position itself as a protector of users' privacy. CEO Tim Cook said earlier this month that the company doesn't want to make users trade their personal information for free services, which makes sense, since Apple doesn't rely on that information to make money.

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